java - 两个集合的并集，操作数组 Java

Question

想法是计算两个集合集合的并集，在程序开始时，会要求用户输入所需集合的长度，然后会提示用户分配集合中的元素，最终的想法是计算联盟。 我已经到达最后，编译程序后仅打印第一组的元素，我真的不知道为什么。

所以我的问题是如何按照我开始的想法计算集合并集。

我的输出:

Desired array lengths: 3 3 First set elements: 1 2 3 Second set elements: 4 5 6 UNION of our sets: 1.002.003

public class Union{

public static void main(String[] args) {
    System.out.println("Desired array lengths: ");
    Scanner scan = new Scanner(System.in);

    //Infinite loop for reading input,if negative number entered break the loop!

    while (true) {
        int n1 = scan.nextInt();
        int n2 = scan.nextInt();
        if (n1 < 0 || n2 < 0)
            break;

        // Assigning elements to the first set.
        double[] s1 = new double[n1];
        System.out.println("First set elements: ");
        //We enter elements as long as the number of the elements added is less than the length of an array we assigned.
        for (int i = 0; i < n1; s1[i++] = scan.nextInt());

            if (n1 == 0)
            System.out.println();//If we do not enter any element go to new line

        //Assigning elements to the second set.
        double[] s2 = new double[n2];
        System.out.println("Second set elements: ");
        for (int i = 0; i < n2; s2[i++] = scan.nextInt());

        if (n2 == 0)
            System.out.println();//Same as before.

        // Calculating union

        double[] s3 = new double[n1 + n2];//We reserve memory space for the s3 array with the size equal to both n1 and n2 arrays.
        int n3 = 0; // Variable used to save number of elements,after reaching the end of the loop n3 WILL HAVE THE SIZE OF N1.
        while (n3 < n1) 
            s3[n3] = s1[n3++];
        for (int j = 0; j < n2; j++) {  //HERE WE ARE CHECKING IF THE ELEMENTS FROM N2 SET ARE PRESENT IN THE N1 
            int i = 0;
            while (i < n1 && s2[j] == s1[i])
                i++;
            if (i == n1)
                s3[n3++] = s2[j];
        }

        double[] pom = new double[n3];
        for (int i = 0; i < n3; pom[i] = s3[i++]);

        s3 = pom;
        pom = null;

        System.out.println("UNION of our sets: ");
        for (int i = 0; i < n3; System.out.printf("%.2f", s3[i++]))
            ;
        System.out.print("\n\n");
    }

}

Answer 1

错误在于您检查 set 的哪些元素的代码中s2 ，您需要输入 set s3 .

基本上你需要检查 set 的元素是否存在s2存在于 set s1 .

因此更改以下代码:

for (int j = 0; j < n2; j++) {  
       int i = 0;
       while (i < n1 && s2[j] == s1[i])
         i++;
       if (i == n1)
         s3[n3++] = s2[j];
}

这段代码:

for (int j = 0; j < n2; j++) {  
       int i = 0;
       while (i < n1 && s2[j] != s1[i])
         i++;
       if (i == n1)
         s3[n3++] = s2[j];
}

循环while (i < n1 && s2[j] != s1[i])将以 i = n1 终止，仅当 set 中没有任何元素时s1 ，与元素 s2[j] 匹配这就是 UNION 中我们想要的元素2 套。